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Reading various other breeders posts I've come to think that incorporating some of the genetics of commercial hybrids in a breeding program to get a good base of disease resistance and tolerance factors, resistance to skin splits, etc. is a good idea.

One of the things I noticed in my grow out of a large number of heirloom and OP varieties this year was that some varieties had much better hang time and shelf life. A home gardener with a few plants would likely not be looking at this as a factor when choosing a variety, but even for the few hundred plants I had this year dealing with the harvest every day became a headache after a while. As I'm looking at partnering with a local charity next year to grow a much larger number of plants I've been considering this factor a lot, and want to incorporate these characteristics into my breeding plans.

What genes are involved in the ESL or LSL hybrids? I'm assuming it involves rin, and as far as I can tell that one doesn't work well in a subsequent generations, you get things like Tom Wagner's Gold Keeper where 25% of the plants fully ripen fruit, 25% will have hard/extra firm fruit and 50% have firm fruit. (this variety and it's percentages used only for example.)

If this is the case, is rin really only useful in F1 hybrids? Are there other genes at work in the ESL or LSL hybrids that might be useful? Or would I be better off looking at OP varieties that exhibit better hang time and shelf life and encorporating them?

There are a couple of regulatory "genes" (transcription factors) that regulate several steps in the pathway of genes controlling fruit ripening. Two have been used some in commercial breeding: rin and nor, with rin the most popular. In the homozygous state both prohibit normal ripening, bu in the heterzygous state give the desired LSL (long shelf life) phenotype. The typical use of these is in the production of F1 hybrids where one of the parents (probably the male parent) is rin/rin and the hybrid is rin/+. Virtually all of the fruit from Mexico picked vine ripe is from rin hybrids. There is no good application of the technology in OP varieties.

I grew the OP version of Keepsake this past year. I picked one that was full sized & had been around a while, so I thought it would ripen quickly in the house. It took 2 weeks to ripen on my kitchen table, and then lasted another 4 weeks on the table, temp around 78-81F. I only have the one data point. I have some seeds saved if you'd like, PM me.